Arrangement of mixing condensers for steam turbine powerplants

ABSTRACT

A system of mixing condensers is provided in which the water levels are maintained at various levels within portions of such mixing condensers connected in series in respect of cooling waters, there being provided at least one pair of mixing condensers, the cooling water sides of which are connected in series and one of which is arranged at a higher level than the other, the cooling water introduced into the mixing condenser of higher level flowing into the mixing condenser of lower level under the action of a hydrostatic pressure difference, the water chamber of the mixing condenser of the higher level forming a vertical downflow conduit having a cross-sectional area which is a fraction of that of the mixing condenser of lower level.

United States Patent ARRANGEMENT 01F MDUNG CUNDENSERS FOR STEAM TUlRlllllNlE POWEWPLANTS 2 (Ilaims, 2 Drawing Figs.

11.8. 1111 261/1419, 60/94 A, 261/36 R, 261/1 16, 261/72 Int. Cl F281) 3/04, F 28b 5/00 Field 01' Swrcli 60/94, 94

3,596fidd [56] References Cited UNITED STATES PATENTS 1,542,545 6/1925 Elliott 60/95 X 3,158,666 11/1964 Helleretal. 261/118 3,391,911 7/1968 Helleretal. 261/118 3,511,481 5/1970 Daltry 261/118 FOREIGN PATENTS 728,512 11/1942 Germany 60/94 Primary Examiner-Tim R. Miles Attorney-Blum, Moscovitz, Friedman & Kaplan ABSTRACT: A system of mixing condensers is provided in which the water levels are maintained at various levels within portions of such mixing condensers connected in series in respect of cooling waters, there being provided at least one pair of mixing condensers, the cooling water sides of which are connected in series and one of which is arranged at a higher level than the other, the cooling water introduced into the mixing condenser of higher level flowing into the mixing condenser of lower level under the action of a hydrostatic pressure difference, the water chamber of the mixing condenser of the higher level forming a vertical downflow conduit having a cross-sectional area which is a fraction of that of the mixing condenser of lower level.

Patented Aug. 3, 1971 3596,88

INVENTOR ATTORNITY ARRANGEMENT Oil MIXING CONDENSEIM limit STEAM 'lllUlitlBllNlE POWEEHWLANTS This invention relates to an arrangement of mixing condensers for steam turbine powerplants.

As is known, up-to-date thermal powerplants are equipped with turbogenerators of possibly high unit power the steam turbines of which are provided with a plurality of outlet stubs for the withdrawing of dead steam. Such steam flows from each outlet stub into individual condensers or into a common condenser where it becomes precipitated. At present, the arrangement is such that condenser portions connected each to an outlet stub of the steam turbine are traversed by cooling water required for precipitating the dead steam in parallel connection so that the same vacuum is generated in all outlet stubs. However, an arrangement is known as well with which the individual condenser portions are traversed by the cooling water in series connection. In this case, the greatest vacuum is generated in the outlet stub at which the cold cooling water enters the system. In the other outlet stubs, the vacuum decreases in correspondence with the warming up of the cooling water. It can be shown that by maintaining a mean value of vacuum obtainable by such series or parallel connection of the various condenser portions traversed by the cooling water of multiflow steam turbines, the heat transmission surface of the condenser may be decreased or, the condenser surface being the same and a higher mean value of vacuum being obtainable, the efficiency of the steam turbine may be increased.

What has been said above applies to mixing condensers of dry cooling tower systems as well with the difference, how ever, that the economical effect of decreasing the heat transmission surface feasible at a certain mean value of vacuum is, in case of mixing condensers, considerably greater than with surface condensers. This is due to the condensation heat being, in case of dry cooling tower systems, transmitted to air which is gaseous medium of very poor heat transmission properties. Therefore, suitable heat transmission surfaces are relatively expensive and, thus, saving is obtained with respect to an expensive portion of the plant which is considerable as regards absolute values.

A series connection of the cooling water of surface condensers requires, as a rule, only that the construction of the condenser be correspondingly changed. A single cooling water pump, however, is sufficient even if the cooling water flows in seriesly connected condenser portions. With mixing condensers, on the other hand, the cooling water traverses the steam chamber of the condenser in the form of a free jet and, therefore, two or more pumps are needed for making the cooling water flow through two or more condenser portions in series connection. However, even in case of mixing condensers connected in series a single pump may be employed if the mixing condenser units disposed each downstream an individual outlet stub are arranged at various levels in such a manner that the cooling water traversing the first mixing condenser arranged at a highest level flows under the action of gravity by free drop into a subsequent condenser arranged at a lower level, etc. The feasibility of such system depends on the level difference required between subsequent condenser portions. This level difference depends, in turn, considerably on the water column height between individual condenser portions or units caused by the vacuum which corresponds to the warming up of the cooling water, and on the flow resistance of the nozzles which serve to form the jets of cooling water. It can be shown if such nozzles are formed in compliance with our US. Pat. No. 3,158,666, their flow resistances do not exceed l to 2 meters water column and, thus, between a pair of seriesly connected mixing condenser portion practically a level difference of at most 3 to 4 meters is required. Thereby, it is rendered possible to operate a system of mixing condensers likewise by a sole cooling water pump in such a manner that a plurality of condenser portions be traversed by the cooling water in series.

it is obvious from what has been explained above that in case of mixing condensers connected in series as regards the cooling water sides water levels of various heights have to be maintained in the condenser portions and, moreover, such water levels have to be controlled in correspondence with the various operational conditions of a respective power plant.

The main object of the present invention is to provide a system of mixing condensers in which the water levels are maintained at various levels within portions of mixing condensers connected in series as regards the cooling water, and controlled in correspondence with various operational conditions of a powerplant. Hereby, a system of seriesly connected mixing condensers is obtained which, due to the aforesaid control of the water levels may be operated by a single circulating pump. For this purpose, the invention provides at least one pair of mixing condensers the cooling water sides of which are connected in series and one of which is arranged at a higher level than the other, the cooling water introduced into the mixing condenser of higher level flowing from it into the mixing condenser of lower level under the action of a hydrostatic pressure difference, and the water chamber of the mixing condenser of higher level forming a vertical downflow conduit having a cross-sectional area which is a fraction of the crosssectional area of the mixing condenser of lower level.

Further objects and details will be described by taking reference to the accompanying drawings in which FIGS. 1 and 2; are connection diagrams of known and new plants, respectively.

FIG. ll shows the connection diagram of a known dry cooling tower powerplant where a double-flow turbine l is employed and the mixing condenser of the plant is composed of two parts or consists of two units 2 and 3 disposed at different levels and connected in series on their cooling water sides. The dead steam of the steam turbine ll becomes condensed by the mixing condenser 2 of higher level and by the mixing condenser 3 of lower level. The cooling water flows through a pipe conduit 19 into the mixing condenser 2 of higher level which is provided at its top with a series of nozzles. The cooling water is discharged through these nozzles and traverses the steam chamber of the condenser 2 in the form of free jets. The water level in condenser 2 of higher level exceeds the level of the nozzles of condenser 3 of lower level by a suitable amount in order to ensure that the pressure difference and the water column height in condenser 2 of higher level be enough for overwhelming the flow resistance within a pipe conduit 4 which connects the water chamber of condenser 2 of higher level with the steam chamber of condenser 3 of lower level, and of nozzles in the latter. The water level appearing in the mixing condenser 3 of lower level is so much higher than the level of circulating pumps 5 that a quiet and bump-free operation of the latter is reliably ensured. The cooling water is delivered by the pumps 5 through heat transmission elements 6, 7, 8 and 9 in which it is cooled down by atmospheric air flowing in the direction of arrows 18. The cooled down cooling water flows in the direction of arrows illustrated in the drawing and arrives in a recuperation water turbine 10 and from here through the pipe conduit W again in the condenser 2 of higher level.

Feed water originating from steam which has been precipitated in the condensers 2 and 3 is fed back into not represented boilers through a pipe conduit 16, passing in its way feed water amount regulators not shown.

With the represented embodiment, a pair of circulating water pumps 5 are shown which, in case of larger plants, are actually arranged in the illustrated manner. It is, however obvious that, from the point of view of connection diagram, the pair of smaller pumps 5 might be replaced by a single pump of higher performance so that the embodiment shown in FIG. 1 complies with the requirement that series connection of the condensers or condenser portions does not require more than one pump.

it will be clear to those skilled in the art that the system shown in FIG. l is sizable and feasible in the usual way for ensuring that, at given operational conditions and circulating water amounts, its working be as required. In practice, however, operational conditions and circulating amounts are liable to variations, and the condenser portions are required to perform their functions even under varying conditions.

The pressures prefailing in the steam chambers of seriesly connected mixing condensers or condenser portions are influenced by the load of the steam turbine and the temperature of the cooling' water which depends, in turn, on whether conditions. Furthermore, the amount of water filling present in the system and the number of heat transmission surfaces disconnected due to mending or to other reasons may cause changes as well. In very huge plants, for reasons of security of operation, more than one circulating pumps will be employed in parallel connection as was the case with the plant shown in FIG. 1. Thus, it may occur that one of both pumps has to be mended and, therewhile, operation has to be kept going by means of a single pump though at circulating a decreased amount of water. Consequently, the control of the water levels in seriesly connected mixing condenser portions has to be provided for all cases possible in the operation of a powerplants of the above-specified nature. Moreover, it has to be ensured that the water filling present in the system should not change, and the amount of water, which corresponds to the amount of dead steam should always be returned in the form of feed water into the boilers of the plant.

Reliable operation of the system according to the invention requires that the water levels in the mixing condensers 2 and 3 should stay within prescribed limits even under operational conditions changing in the above-described manner. Furthermore, it is required, that the amount of feed water necessary for operating the boilers be supplied without interruption. Another requirement is that upon connecting or disconnecting individual heat transmission surfaces changes of the water filling may be compensated. Finally, it is a requirement that the plant operate in the desired manner whether both circulating pumps 5 are working or only one of them is operated.

Such requirements may be met with by means of a control system according to the invention an exemplified embodiment of which is represented in FIG. 2.

The basic idea of controlling the water levels in the seriesly connected condensers of the system is that the water level of the condenser 3 of lower level is kept constant whereas the water level in the condenser 2 of higher level is permitted to change. At the same time, the water receiving capacity of the condenser 3 of lower level is selected much greater than the water receiving capacity of the condenser 2 of higher level. A control means 17 is provided for operating a pair of valves 12 and 13. Upon rising of the water level in mixing condenser 3 of lower level the valve 13 is opened whereas a sinking of the water level entails an opening of valve 12. Through valve 13 water may be discharged from the system into a receptacle 14 under atmospheric pressure. Valve 12 permits to introduce water from the receptacle 14 into the vacuum space of the cooling system. Feed water the amount of which corresponds to the amount of dead steam is abducted through the pipe conduit 16 already mentioned. Control of the amount of the abducted feed water in dependence on the water level within the boilers is carried out by a regulator again not shown.

With the represented embodiment the water level in mixing condenser 2 of higher level is dependent on the flow resistance of the atomizing nozzles of mixing condenser 3 of lower level, on the pressure difference between the steam chambers and on the amount of water circulated through condensers 2 and 3. Upon increasing pressure difference and water amount a higher water level will be installed in mixing condenser 2 of higher level whereas, in the reversed case, the water level decreases therein.

It is seen that mixing condenser 2 of higher level has a bot tom portion 2a of substantially reduced cross-sectional area. Fluctuations of the water level will take place within this bottom portion of reduced cross-sectional area. In contrast, the water chamber of mixing condenser 3 of lower level is suitable for receiving and storing a great amount of water so that surplus amounts of water introduced thereinto entail but small risings of water level. A water reserve necessary for reliable operation of the plant, a bump-free operation of the pumps upon abrupt changes of the characteristics of the water circuit of the system, the possibility of filling up heat exchangers of the plant and, in general, a reliable operation are ensured by such arrangement.

If for instance, besides one pump 5 already in operation, also the other pump 5 is started to work, the control system according to the invention responds as follows:

Upon starting the second circulating pump 5 the amount of water circulated in the cooling system increases by 30 to 50 percent during a relatively short period of time of l to 2 sec. This surplus amount of water is sucked in by the pump 5 from the water chamber of condenser 3 of lower level. In order to obviate bumpings in the operation of the pumps the water level in the condenser 3 of lower level must not substantially decrease. It would be constant if, through the valve 12, a suitable amount of water could abruptly be introduced into the condenser 3 of lower level, or if simultaneously with starting of the second circulating pump 5, more water could flow thereinto through the water chamber 2a of the condenser 2 of higher level and the pipe conduit 4. The first alternative is practically unfeasible because it would require very large valves and quick response. On the other hand, the second alternative takes place only if the water level in the condenser 2 of higher level suddenly rises to a value which is necessary for having the surplus amount of water pressed through the atomizing nozzles of condenser 3 of lower level. In accordance with the present invention, such quick rise of water level in condenser 2 of higher level may be obtained without permitting a substantial decrease of water level in condenser 3 of lower level. This is due to the volume of the water chamber 2a of condenser 2 of higher level being selected but to a fraction of the water chamber of condenser 3 of lower level. Thus, a sudden and substantial water level rise in the water chamber 2a of condenser 2 of higher level may, according to the ratio of cross-sectional areas of the water chambers, be associated with water level decreases in condenser 3 of lower level which may be smaller even by orders of magnitude than the water level rise in the condenser 2 of higher level.

Thus, the control system according to the invention is suitable to ensure a reliable operation even if the amount of water circulating in the water circuit of the system becomes suddenly changed.

A similar phenomenon takes place if in the cooling water circuit a greater number of heat exchangers are connected with respect to a previous number of such heat exchangers or the number of heat exchangers is suddenly decreased by disconnecting several of them. In both cases, any disadvantageous effect of sudden changes of the amount of water traversing the condensers will be eliminated by the control system according to the invention in the already described manner. Obviously, the water chamber of condenser 3 of lower level has to be sized so as to deliver the maximum amount of water filling which may be required in operation of the plant without, however, undergoing a water level decrease greater than permitted. The amount of water used for filling can then be made up for through the valve 12 at a speed which permits to select dimensions of the valve and the water conduits within reasonable and economical limits. The valve 12 of relatively small dimensions will be opened by a feeler of the water level in condenser 3 of lower level whereupon an amount of water required for restoring the original water level therein will flow thereinto.

What we claim is:

1. Control system for steam turbine powerplants having a cooling system consisting of a series connection of more than one mixing condenser wherein one of the mixing condensers is arranged at a higher level than the other, the cooling water introduced into the mixing condenser of higher level flowing from it into the mixing condenser of lower level under the acarranged at a higher level than the other, the cooling water introduced into the mixing condenser of higher level flowing from it into the mixing condenser of lower level under the action of hydrostatic pressure difference, and the mixing condenser of higher level having unitary water chamber located at the bottom thereof and forming a vertical downflow conduit having a cross-sectional area which is a fraction of the cross sectional area of the mixing condenser of lower level, and a water level control operated by a water level in the water chamber of the condenser of lower level, and arranged for introducing water from an exterior receptacle into the system upon decreasing of the water level in the condenser of lower level, and discharging water therefrom into the exterior receptacle upon rising of the water level therein. 

1. Control system for steam turbine powerplants having a cooling system consisting of a series connection of more than one mixing condenser wherein one of the mixing condensers is arranged at a higher level than the other, the cooling water introduced into the mixing condenser of higher level flowing from it into the mixing condenser of lower level under the action of hydrostatic pressure difference, and the mixing condenser of higher level having a unitary water chamber located at the bottom thereof and forming a vertical downflow conduit having a cross-sectional area which is a fraction of the cross-sectional area of the mixing condenser of lower level.
 2. Control system for steam turbine powerplants having a cooling system consisting of a series connection of more than one mixing condenser wherein one of the mixing condensers is arranged at a higher level than the other, the cooling water introduced into the mixing condenser of higher level flowing from it into the mixing condenser of lower level under the action of hydrostatic pressure difference, and the mixing condenser of higher level having unitary water chamber located at the bottom thereof and forming a vertical downflow conduit having a cross-sectional area which is a fraction of the cross-sectional area of the mixing condenser of lower level, and a water level control operated by a water level in the water chamber of the condenser of lower level, and arranged for introducing water from an exterior receptacle into the system upon decreasing of the water level in the condenser of lower level, and discharging water therefrom into the exterior receptacle upon rising of the water level therein. 